1. Field of the Invention
The present invention relates to laminate type batteries used for, for example, robots, electric vehicles, and backup power sources, and battery modules incorporating the laminate type batteries. More particularly, the invention relates to laminate type lithium ion batteries that can improve charge-discharge characteristics at high rate, and battery modules incorporating the laminate type lithium ion batteries.
2. Description of Related Art
In recent years, batteries have been used for not only the power source of mobile information terminal devices such as mobile-phones, notebook computers, and PDAs but also for such applications as robots, electric vehicles, and backup power sources. This has led to a demand for higher capacity batteries. Because of their high energy density and high capacity, lithium ion batteries are widely utilized as the power sources for such applications as described above.
The battery configurations of lithium ion batteries are broadly grouped into two types: one in which a metal battery can in a cylindrical or prismatic shape is used as the battery case, and one in which a laminate film is used as the battery case.
A problem with the lithium-ion battery, particularly with the one using an organic electrolyte solution, has been an increase in the internal pressure that results from abnormal reactions. In view of the problem, the battery using a metal can as the battery case is provided with a gas release valve for releasing a gas to outside and cutting off the electric current when the internal gas pressure increases. On the other hand, the following batteries employing a laminate for the battery case have been proposed, for example. Japanese Published Unexamined Patent Application No. 11-86823 proposes a laminate type battery in which a portion with low proof pressure is provided at a portion of the sealing part so that gas can be released from the portion with low proof pressure when the internal pressure increases. Japanese Published Unexamined Patent Application No. 2007-66612 proposes a laminate type battery in which sealing is effected by a plurality of layers and a pressure sensing element such as pressure sensor or a strain sensor is provided between the plurality of layers so that an increase in the internal pressure can be detected when the sealing peels off.
However, the battery disclosed in Japanese Published Unexamined Patent Application No. 11-86823 has the problem that the release of the gas cannot be prevented in advance because the internal pressure increase cannot be detected before the release of the gas. The battery disclosed in Japanese Published Unexamined Patent Application No. 2007-66612 necessitates provision of a pressure sensor or a strain sensor in the battery, resulting in the problems of poorer battery productivity and higher costs.